The present invention relates to a method of and system for cooling a liquid. More particularly this invention concerns a system employed for cooling water passed through a liquid-heating machine such as a turbine condenser.
Two principal water cooling systems are known, the wet-type system and the dry-type system. In a dry cooler the liquid is cooled purely by heat transfer through a third material. Thus, for instance, water can be passed through a ribbed pipe over which air is circulated, so that heat exchange through the pipe is effected. In the wet-type system a gas is circulated directly in contact with the liquid so as to evaporate a portion of this liquid, thereby taking up the latent heat of evaporation and simultaneously conductively cooling the liquid.
The principal problem with the wet-type system is that the often saturated air used to evaporately cool the water condenses at least partially as it leaves the apparatus and, therefore, forms a large cloud that gives the appearance, although not the actuality, of air pollution. On the other hand the disadvantage of the dry-type system is that it is relatively inefficient so that a great deal of air must be moved over the heat exchanger in order to cool the liquid flowing through it.
It has been suggested to combine these two systems in order to reduce the overall humidity of the air released to the atmosphere. This has been done invariably by simply arranging a wet-type cooler in series relative to the direction of flow of the liquid through the system with a dry-type cooler. This is most simply done by providing in the upper region of an evaporative type cooling tower a plurality of ribbed tubes constituting a dry-type heat exchanger. Air streams are drawn in over each of these coolers and the heated air from the dry-type cooler is mixed with the heated and humidified air from the wet-type cooler and then released to the atmosphere. Thus the relative humidity is considerably decreased so that an objectionable cloud is not formed directly at the outlet of the system.
In such arrangements all the water issuing from the turbine condenser is first passed through the dry-type cooler, and then fed to the wet-type cooler. In the wet-type cooler the water is allowed to trickle down counter-current to a rising current of air and is then gathered in a basin beneath the wet-type cooler. From the basin the water is recirculated back to the turbine condenser.
The principal difficulty with such arrangements is that it is necessary to provide an extremely large dry-type heat exchange, so that original installation costs are very high. Furthermore, the operating efficiency is frequently considerably less than that which is ideally desired, so that the advantages on the one hand are often frequently completely outweighed by the disadvantages of such a combination system.